1. Field of the Invention
The present invention relates to a method for producing a core sand and/or mold sand for foundry purposes, according to which a granular mineral mold base material is mixed with an inorganic additive and an inorganic binder.
Core sands for foundry purposes are generally used to define cores in cast pieces. In contrast, mold sand generally means a sand or sand-like mold base material that determines the outer shape of the desired cast piece. The terms core sand and mold sand are covered, for the most part, by the general term foundry sand or foundry mold base material, which means that the present case concerns itself not necessarily with sands but rather with granular foundry mold materials in general.
2. The Prior Art
In the production of core sands and/or mold sands for foundry purposes, usually, in addition to a binder such as bentonite, for example, a glance carbon forming agent or, in general, coal dust/hydrocarbon resin is added, as is described, for example, in DE 30 17 119 A1. Coal dust is used in the implementation of foundry sands essentially because an improved casting surface is achieved, and sand adhesions are avoided, to a great extent. Furthermore, the casting mold can be advantageously separated from the sand, and casting defects are reduced. Finally, metering can be performed in simple manner, and the costs are relatively slight.
These advantages, however, are achieved at the cost of disadvantages. For example, the strength of the casting mold suffers as the result of the dust addition. Also, harmful emissions resulting from the organic components in the foundry mold sand or foundry mold base material, for example carbon monoxide or sulfur dioxide, as well as benzene emissions, are observed. Furthermore, it cannot be prevented that the mold base material or mold sand, which is generally circulated and processed again, becomes contaminated, specifically by organic condensation products, benzene, and so forth. Furthermore, an increasing moisture content is observed, which can result in casting defects.
A method having the configuration described initially is presented, in terms of approach, in U.S. Pat. No. 2,828,214. Here, Example II discloses a composition for casting core molds and molds, which consists of sand, binders, and additives that are mixed. Additives on an organic basis, for example containing cellulose, are used. As a result, emissions must still be feared, and, in the final analysis, casting defects, as described, cannot be precluded. The present invention seeks to provide a remedy on the whole to these drawbacks.